Avian Community Responses to Bison Grazing in North American Intermountain Grasslands

Author

Danielle A. Fagre, University of Montana, MissoulaFollow

Year of Award

2018

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Wildlife Biology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Dr. Victoria Dreitz

Commitee Members

Dr. Mark Hebblewhite, Dr. Dean Pearson

Keywords

songbirds, grassland, shrubland, bison, grazing, Yellowstone National Park, National Bison Range

Subject Categories

Biology | Ecology and Evolutionary Biology | Terrestrial and Aquatic Ecology

Abstract

Grassland and shrubland songbird species are a guild of conservation concern in North America. Many of these species have experienced severe population declines, due to habitat loss and land use change. This makes the conservation and management of remaining habitat of crucial importance for this guild. Grazing by large herbivores is an ecosystem process in grassland systems, and in North America, one of the major historic grazers was the Plains bison (Bison bison). Bison are considered ecosystem engineers, because they modify habitat to be more or less suitable for other species, such as grassland and shrubland songbirds. Bison grazing can affect avian habitat by altering the vegetation structure. In turn, birds respond to these changes in vegetation structure. Bison are becoming more common due to recent reintroductions. From 2009-2017, at least eight bison reintroductions have occurred in North America. Lands where bison exist are good candidates for songbird conservation because bison are typically present in protected areas with a large grass and shrub component. Despite this potential, there is limited research about the effects of bison grazing on grassland and shrubland songbirds. Further research on this subject will inform bison management for songbird conservation. I investigate the relationship between bison grazing and songbird responses in two intermountain grasslands: the National Bison Range and Yellowstone National Park. In Chapter 1, I explore two ecological processes that may maintain species richness of grassland and shrubland songbirds: habitat heterogeneity from bison grazing, and productivity, a measure of the resources available to individuals. I analyzed the relationship between these variables and the occupancy of 10 avian species. I conclude that bison grazing has a stronger influence on bird occupancy and species richness than site productivity. In Chapter 2, I test whether differences between the study sites influence the abundance responses of vesper sparrow (Pooecetes gramineus) and western meadowlark (Sturnella neglecta) to bison grazing intensity. The differences, such as scale of bison grazing, herd size and density, and vegetation type show minimal influence on these species’ responses to bison grazing, but may be worth considering in conservation applications.

Recommended Citation

Fagre, Danielle A., "Avian Community Responses to Bison Grazing in North American Intermountain Grasslands" (2018). Graduate Student Theses, Dissertations, & Professional Papers. 11213.
https://scholarworks.umt.edu/etd/11213